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Abstract:

A multi-carrier cellular wireless network (400) employs base stations
(404) that transmit two different groups of pilot subcarriers: (1)
cell-specific pilot subcarriers, which are used by a receiver to extract
information unique to each individual cell (402), and (2) common pilots
subcarriers, which are designed to possess a set of characteristics
common to all the base stations (404) of the system. The design criteria
and transmission formats of the cell-specific and common pilot
subcarriers are specified to enable a receiver to perform different
system functions. The methods and processes can be extended to other
systems, such as those with multiple antennas in an individual sector and
those where some subcarriers bear common network/system information.

Claims:

1. A transmitting method for a base station in a cell within a group of
cells in an orthogonal frequency division multiplexing system, the base
station having multiple transmission branches, the method comprising:
transmitting cell-specific pilot subcarriers, in accordance with a
transmission diversity scheme or a multiple-input multiple-output scheme,
wherein some of the cell-specific pilot subcarriers are not aligned in
frequency subcarrier index with cell-specific pilot subcarriers
transmitted by another base station in the group of cells; transmitting
common pilot subcarriers in accordance with a common pilot transmission
scheme, wherein: the common pilot subcarriers are aligned in frequency
subcarrier index with common pilot subcarriers transmitted by other base
stations in the group of cells; a ratio of an amplitude (ai,m and
an,m) of two common pilot subcarriers having a same time index
(tk) that are transmitted via a common transmission branch is a
constant for the group of cells; and a difference of a phase
(φi,m and (φn,m) of two common pilot subcarriers having
a same time index (tk) that are transmitted via a common
transmission branch is a constant for the group of cells; and controlling
independently a transmission power of the cell-specific pilot subcarriers
and a transmission power of the common pilot subcarriers.

2. The method of claim 1, wherein the transmission power of the
cell-specific pilot subcarriers is higher than the transmission power of
the common pilot subcarriers.

3. The method of claim 1, wherein the transmission power of the
cell-specific pilot subcarriers is lower than the transmission power of
the common pilot subcarriers.

4. The method of claim 1, wherein the cell-specific pilot subcarriers
enable a mobile station in the cell to determine channel coefficients for
a channel from the base station to the mobile station.

5. The method of claim 1, wherein the specific amplitudes, phases, and
frequency subcarrier indices of the cell-specific pilot subcarriers
enable a mobile station in the cell to differentiate the cell-specific
pilot subcarriers from pilot subcarriers transmitted by base stations in
other cells.

6. The method of claim 1, wherein the common pilot subcarriers enable a
mobile station in the cell to determine composite channel coefficients
for a composite channel, the composite channel corresponding to an
aggregate of different channels from base stations in the group of cells
to the mobile station.

7. In a cell within a group of cells in an orthogonal frequency division
multiplexing system, a base station having multiple transmission
branches, the base station comprising: a first transmitter component that
is configured to transmit cell-specific pilot subcarriers, in accordance
with a transmission diversity scheme or a multiple-input multiple-output
scheme, wherein some of the cell-specific pilot subcarriers are not
aligned in frequency subcarrier index with cell-specific pilot
subcarriers transmitted by another base station in the group of cells; a
second transmitter component that is configured to transmit common pilot
subcarriers in accordance with a common pilot transmission scheme,
wherein: the common pilot subcarriers are aligned in frequency subcarrier
index with common pilot subcarriers transmitted by other base stations in
the group of cells; a ratio of an amplitude (ai,m and an,m) of
two common pilot subcarriers having a same time index (tk) that are
transmitted via a common transmission branch is a constant for the group
of cells; and a difference of a phase (φi,m and (φn,m)
of two common pilot subcarriers having a same time index (tk) that
are transmitted via a common transmission branch is a constant for the
group of cells; and a controller component that is configured to control
independently a transmission power of the cell-specific pilot subcarriers
and a transmission power of the common pilot subcarriers.

8. The base station of claim 7, wherein the transmission power of the
cell-specific pilot subcarriers is higher than the transmission power of
the common pilot subcarriers.

9. The base station of claim 7, wherein the transmission power of the
cell-specific pilot subcarriers is lower than the transmission power of
the common pilot subcarriers.

10. The base station of claim 7, wherein the cell-specific pilot
subcarriers enable a mobile station in the cell to determine channel
coefficients for a channel from the base station to the mobile station.

11. The base station of claim 7, wherein the specific amplitudes, phases,
and frequency subcarrier indices of the cell-specific pilot subcarriers
enable a mobile station in the cell to differentiate the cell-specific
pilot subcarriers from pilot subcarriers transmitted by base stations in
other cells.

12. The base station of claim 7, wherein the common pilot subcarriers
enable a mobile station in the cell to determine composite channel
coefficients for a composite channel, the composite channel corresponding
to an aggregate of different channels from base stations in the group of
cells to the mobile station.

Description:

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation of, and incorporates herein by
reference in its entirety. U.S. patent application Ser. No. 13/212,116,
entitled "METHODS AND APPARATUS USING CELL-SPECIFIC AND COMMON PILOT
SUBCARRIERS IN MULTI-CARRIER, MULTI-CELL WIRELESS COMMUNICATION
NETWORKS," filed Aug. 17, 2011, which is a continuation of, and
incorporates herein by reference in its entirety. U.S. patent application
Ser. No. 10/583,530, entitled "METHODS AND APPARATUS USING CELL-SPECIFIC
AND COMMON PILOT SUBCARRIERS IN MULTI-CARRIER, MULTI-CELL WIRELESS
COMMUNICATION NETWORKS," filed May 30, 2007 which is a U.S. National
Stage of PCT Application No. PCT/US05/01939, entitled "METHODS AND
APPARATUS FOR MULTI-CARRIER, MULTI-CELL WIRELESS COMMUNICATION NETWORKS,"
filed Jan. 20, 2005, which claims the benefit of and priority to U.S.
Provisional Patent Application No. 60/540,032, entitled "METHODS AND
APPARATUS FOR MULTI-CARRIER, MULTI-CELL WIRELESS COMMUNICATION NETWORKS,"
filed on Jan. 29, 2004.

BACKGROUND

[0002] In multi-carrier wireless communications, many important system
functions such as frequency synchronization and channel estimation,
depicted in FIG. 1, are facilitated by using the network information
provided by a portion of total subcarriers such as pilot subcarriers. The
fidelity level of the received subcarriers dictates how well these
functions can be achieved, which in turn affect the efficiency and
capacity of the entire network.

[0003] In a wireless network, there are a number of base stations, each of
which provides coverage to designated areas, normally called a cell. If a
cell is divided into sectors, from a system engineering point of view
each sector can be considered a cell. In this context, the terms "cell"
and "sector" are interchangeable. The network information can be
categorized into two types: the cell-specific information that is unique
to a particular cell, and the common information that is common to the
entire network or to a portion of the entire networks such as a group of
cells.

[0004] In a multi-cell environment, for example, the base station
transmitter of each cell transmits its own pilot subcarriers, in addition
to data carriers, to be used by the receivers within the cell. In such an
environment, carrying out the pilot-dependent functions becomes a
challenging task in that, in addition to the degradation due to multipath
propagation channels, signals originated from the base stations at
different cells interfere with each other.

[0005] One approach to deal with the interference problem has been to have
each cell transmit a particular pattern of pilot subcarriers based on a
certain type of cell-dependent random process. This approach, to a
certain degree, has mitigated the impact of the mutual interference
between the pilot subcarriers from adjacent cells; however, it has not
provided for a careful and systematic consideration of the unique
requirements of the pilot subcarriers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 depicts a basic multi-carrier wireless communication system
consisting of a transmitter and a receiver.

[0007] FIG. 2 shows basic structure of a multi-carrier signal in the
frequency domain, which is made up of subcarriers.

[0008] FIG. 3 shows a radio resource divided into small units in both the
frequency and time domains: subchannels and time slots.

[0009] FIG. 4 depicts a cellular wireless network comprised of multiple
cells, in each of which coverage is provided by a base station (BS).

[0011] FIG. 6 is an embodiment of pilot-generation-and-insertion
functional block shown in FIG. 1, which employs a microprocessor to
generate pilot subcarriers and insert them into a frequency sequence
contained in the electronic memory.

[0012] FIG. 7 shows that common pilot subcarriers are generated by a
microprocessor of FIG. 6 to realize phase diversity.

[0013] FIG. 8 is an embodiment of delay diversity, which effectively
creates phase diversity by adding a random delay time duration, either in
baseband or RF, to the time-domain signals.

[0015] FIG. 10 is an embodiment of synchronization in frequency and time
domains of two collocated base stations sharing a common frequency
oscillator.

[0016] FIG. 11 is an embodiment of synchronization in frequency and time
domains with base stations at different locations sharing a common
frequency reference signal generated from the GPS signals.

[0017] FIG. 12 is an embodiment depicting a wireless network consisting of
three groups of cells (or sectors) and base stations in each group that
share their own set of common pilot subcarriers.

[0018] FIG. 13 shows all base stations within a network transmit, along
with a common pilot subcarrier, a data subcarrier carrying data
information common to all cells in the network.

DETAILED DESCRIPTION

[0019] In the following description the invention is explained with
respect to some of its various embodiments, providing specific details
for a thorough understanding and enablement. However, one skilled in the
art will understand that the invention may be practiced without such
details. In other instances, well-known structures and functions have not
been shown or described in detail to avoid obscuring the depiction of the
embodiments.

[0020] Unless the context clearly requires otherwise, throughout the
description and the claims, the words "comprise," "comprising," and the
like are to be construed in an inclusive sense as opposed to an exclusive
or exhaustive sense; that is to say, in the sense of "including, but not
limited to." Words using the singular or plural number also include the
plural or singular number respectively. Additionally, the words "herein,"
"above," "below" and words of similar import, when used in this
application, shall refer to this application as a whole and not to any
particular portions of this application. When the claims use the word
"or" in reference to a list of two or more items, that word covers all of
the following interpretations of the word: any of the items in the list,
all of the items in the list and any combination of the items in the
list.

[0021] FIG. 1 depicts a basic multi-carrier wireless communication system
consisting of a transmitter 102 and a receiver 104. A functional block
106 at the transmitter, called Pilot generation and insertion, generates
pilot subcarriers and inserts them into predetermined frequency
locations. These pilot subcarriers are used by the receiver to carry out
certain functions. In aspects of this invention, pilot subcarriers are
divided into two different groups according to their functionalities, and
hence their distinct requirements. The transmission format of each group
of pilot subcarriers will be designed so that it optimizes the
performance of the system functions such as frequency synchronization and
channel estimation.

[0022] The first group is called "cell-specific pilot subcarriers," and
will be used by the receiver 104 to extract information unique to each
individual cell. For example, these cell-specific pilot subcarriers can
be used in channel estimation where it is necessary for a particular
receiver to be able to differentiate the pilot subcarriers that are
intended for its use from those of other cells. For these pilot
subcarriers, counter-interference methods are necessary.

[0023] The second group is termed "common pilot sub-carriers," and are
designed to possess a set of characteristics common to all base stations
of the system. Thus, every receiver 104 within the system is able to
exploit these common pilot subcarriers to perform necessary functions
without interference problem. For instance, these common pilot
subcarriers can be used in the frequency synchronization process, where
it is not necessary to discriminate pilot subcarriers of different cells,
but it is desirable for the receiver to combine coherently the energy of
common pilot subcarriers with the same carrier index from different
cells, so as to achieve relatively accurate frequency estimation.

[0024] Aspects of this invention provide methods to define the
transmission formats of the cell-specific and common pilot subcarriers
that enable a receiver to perform different system functions. In
particular, a set of design criteria are provided for pilot subcarriers.
Other features of this invention further provide apparatus or means to
implement the above design processes and methods. In particular, signal
reception can be improved by manipulating phase values of the pilot
subcarriers and by using power control.

[0025] The methods and processes can also be extended to other cases, such
as where multiple antennas are used within an individual sector and where
some subcarriers are used to carry common network/system information.
Base stations can be synchronized in frequency and time by sharing a
common frequency oscillator or a common frequency reference signal, such
as the one generated from the signals provided by the Global Positioning
System (GPS).

Multi-Carrier Communication System

[0026] In a multi-carrier communication system such as multi-carrier code
division multiple access (MC-CDMA) and orthogonal frequency division
multiple access (OFDMA), information data are multiplexed on subcarriers
that are mutually orthogonal in the frequency domain. In effect, a
frequency selective channel is broken into a number of parallel but small
segments in frequency that can be treated as flat fading channels and
hence can be easily dealt with using simple one-tap equalizers. The
modulation/demodulation can be performed using the fast Fourier transform
(FFT).

[0027] In a multi-carrier communication system the physical media resource
(e.g., radio or cable) can be divided in both the frequency and the time
domains. This canonical division provides a high flexibility and fine
granularity for resource sharing. The basic structure of a multi-carrier
signal in the frequency domain is made up of subcarriers, and within a
particular spectral band or channel there are a fixed number of
subcarriers. There are three types of subcarriers:

[0028] 1. Data subcarriers, which carry information data;

[0029] 2. Pilot subcarriers, whose phases and amplitudes are predetermined
and made known to all receivers and which are used for assisting system
functions such as estimation of system parameters; and

[0030] 3. Silent subcarriers, which have no energy and are used for guard
bands and DC carriers.

[0031] The data subcarriers can be arranged into groups called subchannels
to support multiple access and scalability. The subcarriers forming one
subchannel are not necessarily adjacent to each other. This concept is
illustrated in FIG. 2, showing a basic structure of a multi-carrier
signal 200 in the frequency domain, which is made up of subcarriers. Data
subcarriers can be grouped into subchannels in a particular way. The
pilot subcarriers are also distributed over the entire channel in a
particular way.

[0032] The basic structure of a multi-carrier signal in the time domain is
made up of time slots to support multiple-access. The resource division
in both the frequency and time domains is depicted in FIG. 3 which shows
a radio resource divided into small units in both the frequency and time
domains: subchannels and time slots, 300. The basic structure of a
multi-carrier signal in the time domain is made up of time slots.

[0033] As depicted in FIG. 1, in a multi-carrier communication system, a
generic transmitter may consist of the following functional blocks:

[0034] 1. Encoding and modulation 108

[0035] 2. Pilot generation and insertion 106

[0036] 3. Inverse fast Fourier transform (IFFT) 110

[0037] 4. Transmission 112

And a generic receiver may consist of the following functional blocks:

[0038] 1. Reception 114

[0039] 2. Frame synchronization 116

[0040] 3. Frequency and timing compensation 118

[0041] 4. Fast Fourier transform (FFT) 120

[0042] 5. Frequency, timing, and channel estimation 122

[0043] 6. Channel compensation 124

[0044] 7. Decoding 126

Cellular Wireless Networks

[0045] In a cellular wireless network, the geographical region to be
serviced by the network is normally divided into smaller areas called
cells. In each cell the coverage is provided by a base station. Thus,
this type of structure is normally referred to as the cellular structure
depicted in FIG. 4, which illustrates a cellular wireless network 400
comprised of multiple cells 402, in each of which coverage is provided by
a base station (BS) 404. Mobile stations are distributed within each
coverage area.

[0046] A base station 404 is connected to the backbone of the network via
a dedicated link and also provides radio links to mobile stations within
its coverage. A base station 404 also serves as a focal point to
distribute information to and collect information from its mobile
stations by radio signals. The mobile stations within each coverage area
are used as the interface between the users and the network.

[0047] In an M-cell wireless network arrangement, with one-way or two-way
communication and time division or frequency division duplexing, the
transmitters at all the cells are synchronized via a particular means and
are transmitting simultaneously. In a specific cell 402 of this
arrangement, the pth cell, a receiver receives a signal at a specific
subcarrier, the ith subcarrier, at the time tk, which can be
described as:

where ai,m(tk) and φi,m(tk) denote the signal
amplitude and phase, respectively, associated with the ith
subcarrier from the base station of the mth cell.

Cell-Specific Pilot Subcarriers

[0048] If the ith subcarrier is used as a pilot subcarrier at the pth cell
for the cell-specific purposes, the cell-specific information carried by
ai,p(tk)) and φi,p(tk)) will be of interest to
the receiver at the pth cell and other signals described by the second
term on the right hand side of equation (1) will be interference, which
is an incoherent sum of signals from other cells. In this case, a
sufficient level of the carrier-to-interference ratio (CIR) is required
to obtain the estimates of ai,p(tk)) and
φi,p(tk)) with desirable accuracy.

[0049] There are many ways to boost the CIR. For examples, the amplitude
of a pilot subcarrier can be set larger than that of a data subcarrier;
power control can be applied to the pilot subcarriers; and cells adjacent
to the pth cell may avoid using the ith subcarrier as pilot subcarrier.
All these can be achieved with coordination between the cells based on
certain processes, described below.

Common Pilot Subcarriers

[0050] The common pilot subcarriers for different cells are normally
aligned in the frequency index at the time of transmission, as depicted
in FIG. 5, which shows pilot subcarriers divided into two groups:
cell-specific pilot sub-carriers and common pilot subcarriers. The
cell-specific pilot subcarriers for different cells are not necessarily
aligned in frequency. They can be used by the receiver to extract
cell-specific information. The common pilot subcarriers for different
cells may be aligned in frequency, and possess a set of attributes common
to all base stations within the network. Thus, every receiver within the
system is able to exploit these common pilot subcarriers without
interference problem. The power of the pilot subcarriers can be varied
through a particular power control scheme and based on a specific
application.

[0051] If the ith subcarrier is used as a pilot subcarrier at the pth cell
for the common purposes, it is not necessary to consider the second term
on the right hand side of equation (1) to be interference. Instead, this
term can be turned into a coherent component of the desirable signal by
designing the common pilot carriers to meet the criteria specified in the
aspects of this invention, provided that base stations at all cells are
synchronized in frequency and time. In such a case the cell in which the
receiver is located becomes irrelevant and, consequently, the received
signal can be rewritten as:

The common pilot subcarriers can be used for a number of functionalities,
such as frequency offset estimation and timing estimation.

[0052] To estimate the frequency, normally signals at different times are
utilized. In an example with two common pilot subcarriers of the same
frequency index, the received signal at time tk+1, with respect to
the received signal at time tk, is given by

where Δf=fn-fi and Ts denotes the sampling period.
If Δf is much less than the coherence bandwidth of the channel and

αi,m(tk)=c(tk)αn,m(tk) (8)

and

φi,m(tk)=φn,m(tk)+γ(tk) (9)

then Ts can be determined by

2πΔfTs(tk)=arg{si*(tk)sn(tk)}-.ga-
mma.(tk) (10)

where c(tk)>0 and -π≦γ(tk)≦π are
predetermined constants for all values of m.

[0054] FIG. 6 is an embodiment of pilot-generation-and-insertion
functional block 106 shown in FIG. 1, which employs a microprocessor 602
to generate pilot subcarriers and insert them into a frequency sequence
contained in electronic memory 604. In one embodiment of the invention
illustrated in FIG. 6, a microprocessor 602 embedded in the
pilot-generation-and-insertion functional block 106 computes the
attributes of the pilot subcarriers such as their frequency indices and
complex values specified by their requirements, and insert them into the
frequency sequence contained in the electronic memory 604, such as a RAM,
ready for the application of IFFT.

Diversity for Common Pilot Subcarriers

[0055] Considering equation (2), which is the sum of a number of complex
signals, it is possible for these signals to be destructively
superimposed on each other and cause the amplitude of the receiver signal
at this particular subcarrier to be so small that the signal itself
becomes unreliable. Phase diversity can help this adverse effect. In the
example of frequency estimation, a random phase θl,m can be
added to another pilot subcarrier, say the Ith subcarrier, which results
in

φl,m(tk)=φi,m(tk)+θl,m (11)

and

φl,m(tk+1)=φi,m(tk+1)+θl,m (12)

where θl,m should be set differently for each cell, and
provided that the following condition is met,

φl,m(tk)=φl,m(tk+1)+βl, for all
values of m (13)

[0056] With the phase diversity, it is expected that the probability of
both |si(tk)| and |si(tk)| diminishing at the same
time is relatively small. The embodiment of phase diversity is depicted
in FIG. 7, which shows common pilot subcarriers generated by a
microprocessor of FIG. 6 to realize phase diversity. It should be noted
that time delay will achieve the equivalent diversity effect.

[0057] Another embodiment is illustrated in FIG. 8, which effectively
creates phase diversity by adding a random delay time duration 802,
either in baseband or RF, to the time-domain signals.

Power Control for Pilot Subcarriers

[0058] In one embodiment of the invention, power control can be applied to
the pilot subcarriers. The power of the pilot subcarriers can be adjusted
individually or as a subgroup to

In another embodiment power control is implemented differently for
cell-specific pilot subcarriers and common pilot subcarriers. For
example, stronger power is applied to common pilot subcarriers than to
the cell-specific subcarriers.

Application to Multiple Antennas

[0062] The methods and processes provided by this invention can also be
implemented in applications where multiple antennas are used within an
individual sector, provided that the criteria specified either by
equations (4) and (5) for frequency estimation or by equations (8) and
(9) for timing estimation are satisfied.

[0063] FIG. 9 shows two examples for extension to multiple antenna
applications. In case (a) where there is only one transmission branch
that is connected to an array of antennas 902 through a transformer 904
(e.g., a beam-forming matrix), the implementation is exactly the same as
in the case of single antenna. In case (b) of multiple transmission
branches connected to different antennas 906 (e.g., in a transmission
diversity scheme or a multiple-input multiple-output scheme), the
cell-specific pilot subcarriers for transmission branches are usually
defined by a multiple-antenna scheme whereas the common pilot subcarriers
for each transmission branch are generated to meet the requirements of
(4) and (5) for frequency estimation or (8) and (9) for timing
estimation.

Joint-Use of Cell-Specific and Common Pilot Subcarriers

[0064] In one embodiment the cell-specific and common pilot subcarriers
can be used jointly in the same process based on certain information
theoretic criteria, such as the optimization of the signal-to-noise
ratio. For example, in the estimation of a system parameter (e.g.
frequency), some or all cell-specific subcarriers, if they satisfy a
certain criterion, such as to exceed a CIR threshold, may be selected to
be used together with the common pilot subcarriers to improve estimation
accuracy. Furthermore, the common pilot sub-carriers can be used along
with the cell-specific subcarriers to determine the cell-specific
information in some scenarios, one of which is the operation at the edge
of the network.

Base Transmitters Synchronization

[0065] Base stations at all cells are required to be synchronized in
frequency and time. In one embodiment of the invention the collocated
base station transmitters are locked to a single frequency oscillator, as
in the case where a cell is divided into sectors and the base stations of
these sectors are physically placed at the same location.

[0066] FIG. 10 is an embodiment of synchronization in frequency and time
domains of two collocated base stations sharing a common frequency
oscillator 1002. Mobile stations 1004 covered by these two base stations
do not experience interference when receiving the common pilot
subcarriers. The base station transmitters that are located at different
areas are locked to a common reference frequency source, such as the GPS
signal. FIG. 11 depicts an embodiment of synchronization in frequency and
time domains with base stations 1102 and 1104 at different locations
sharing a common frequency reference signal generated from the GPS 1106
signals. Mobile stations 1108 covered by these two base stations 1102 and
1104 do not experience interference when receiving the common pilot
subcarriers.

[0067] In some applications, the entire wireless network may consist of
multiple groups of cells (or sectors) and each group may have its own set
of common pilot subcarriers. In such scenarios, only those base stations
within their group are required to synchronize to a common reference.
While the common pilot subcarriers within each group are designed to meet
the criteria defined by equations (4) and (5) or by (8) and (9) for the
use by its base stations, a particular counter-interference process
(e.g., randomization in frequency or power control) will be applied to
different sets of common pilot subcarriers. This will cause the signals
from the cells within the same group to add coherently while the signals
from the cells in other groups are treated as randomized interference.

[0068] One embodiment of such implementation is illustrated in FIG. 12,
where a wireless network consists of three groups (A, B, and C) of cells
(or sectors). The base stations within their own group share the same set
of common pilot subcarriers. In this scenario, only those base stations
within their group are required to synchronize to a common reference.
While the common pilot subcarriers within each group are designed to meet
the criteria defined in this invention, a particular counter-interference
process (e.g., randomization in frequency) will be applied to different
sets of common pilot subcarriers. For example, the base stations at Cells
A1, A2, and A3 in Group A synchronize to their own common reference
source and transmit the same set of common pilot subcarriers; and the
base stations at Cells B1, B2, and B3 in Group B synchronize to their own
reference source and transmit another set of common pilot subcarriers
that are located at different places in the frequency domain.

Extension to Transmission of Data Information

[0069] All design processes, criteria, and methods described in the
embodiments of this invention can be extended to applications where
common network information is required to be distributed to all receivers
within the network. In one example, all the base stations within the
network transmit, along with some common pilot subcarriers, an identical
set of data subcarriers in which the data information common to all the
cells in the network is imbedded.

[0070] FIG. 13 shows all base stations within a network transmit, along
with a common pilot subcarrier, a data subcarrier carrying data
information common to all cells in the network. A receiver within the
network can determine the composite channel coefficient based on the
common pilot subcarrier and apply it to the data subcarrier to compensate
for the channel effect, thereby recovering the data information.

[0071] The above detailed descriptions of embodiments of the invention are
not intended to be exhaustive or to limit the invention to the precise
form disclosed above. While specific embodiments of, and examples for,
the invention are described above for illustrative purposes, various
equivalent modifications are possible within the scope of the invention,
as those skilled in the relevant art will recognize. For example, while
steps are presented in a given order, alternative embodiments may perform
routines having steps in a different order. The teachings of the
invention provided herein can be applied to other systems, not
necessarily the system described herein. These and other changes can be
made to the invention in light of the detailed description.

[0072] The elements and acts of the various embodiments described above
can be combined to provide further embodiments.

[0073] These and other All of the above U.S. patents and applications and
other references are incorporated herein by reference. Aspects of the
invention can be modified, if necessary, to employ the systems, functions
and concepts of the various references described above to provide yet
further embodiments of the invention.

[0074] Changes can be made to the invention in light of the above detailed
description. In general, the terms used in the following claims should
not be construed to limit the invention to the specific embodiments
disclosed in the specification, unless the above detailed description
explicitly defines such terms. Accordingly, the actual scope of the
invention encompasses the disclosed embodiments and all equivalent ways
of practicing or implementing the invention under the claims.

[0075] While certain aspects of the invention are presented below in
certain claim forms, the inventors contemplate the various aspects of the
invention in any number of claim forms. For example, while only one
aspect of the invention is recited as embodied in a computer-readable
medium, other aspects may likewise be embodied in a computer-readable
medium. Accordingly, the inventors reserve the right to add additional
claims after filing the application to pursue such additional claim forms
for other aspects of the invention.

Patent applications by Haiming Huang, Bellevue, WA US

Patent applications by Kemin Li, Bellevue, WA US

Patent applications by Titus Lo, Bellevue, WA US

Patent applications by Xiaodong Li, Kirkland, WA US

Patent applications by NEOCIFIC, INC.

Patent applications in class Having both time and frequency assignment

Patent applications in all subclasses Having both time and frequency assignment